Process of tanning skins with acidic solutions of alkali metal zirconium silicates



United States PatefitO PROCESS OF TANNING SKINS WITH ACIDIC SOLUTIONS OF ALKALI METAL ZIRCO- NIUM SILICATES William J. Ran, Glenside, and Ian C. Somerville, Willow Grove, Pa., assignors to Rohm & Haas Company, Philadelphia, Pa., a corporation of Delaware No Drawing. Application May 18, 1954 Serial No. 430,732

12 Claims. (Cl. 8-94.25)

This invention relatesto the tanning of animal hides or skins with zirconium compounds to produce leather, and it is particularly concerned with the tanning of such skins by means of water-insoluble double silicates of zirconium and alkali metals.

The tanning of skins with water-soluble zirconium salts has long been known. Such salts are quite expensive with the result that a zirconium tannage generally costs about three to five times as much as chromium tannage for the production of leathers. It has long been desired to use less expensive zirconium compounds for tanning skins and the cheapest compounds of zirconium that are convertible to a Water-soluble tanning salt are the double silicates of zirconium with sodium. However, these silicates have heretofore generally been avoided in tanning operations because of disadvantages, such as the fact that silicic acid tannage of leather tends to produce a combination of the silica with'the protein of the skin which becomes embrittledv with age. Accordingly, in previous tannagcs using double silicates, certain precautions have been taken to overcome the disadvantages encountered; For example, organic compounds of hydrogen bonding donor type have been included in the tanning bath for controlling the tannage. In another instance, a water-soluble zirconium salt absorbed in and thereby surrounded by a protective silica gel is produced by reacting a sodium silico-zirconate with a strong mineral acid, such as sulfuric acid or hydrochloric acid, at elevated temperatures from 60 C. to about 105 C. Accordingly, these precautionary measures require additional expense. I

It has now been discovered that certain water-insoluble alkali metal zirconium silicates can be introduced directly into an aqueous acidic tanning liquor in the pres ence of the skin to be tanned with the production of leather having all of the qualities of a zirconium-tanned leather produced by water-soluble zirconium salts in the absence of silicic acid. Surprisingly, the leather obtained lacks the disadvantageous character normally obtained when tannage is effected in the presence of. silicic acid and in some cases the quality of the leather obtained is somewhat better even than that obtained with watersoluble zirconium salts in the absence of silicic acid, in

respect to plumpness, mellowness, and fullness.

The double silicates of zirconium and the alkali metals that may be used in accordance with the present invention are those in which the molar ratio of SiO :ZrO is not over 1.5: l and is preferably about 1:1,;and in which the ratio of silica to the oxide of the alkali metal is not over 3:1 and preferably is about 1:1. Such double silicates may be obtained from naturally or artificially produced zirconium minerals or compounds by sintering with the appropriate amountof an alkali metal carbonate, such as the carbonate of sodium, potassium, or' lithium or preferably that of sodium from the cost standpoint. For example, zircon or zircon sand or beccarite may be sintered with the appropriate amount of the alkali metal carbonate. Depending upon the purity of the minerals and the proportions of silica andzirconium oxide com- Patented Mar. 11, 1958 fall Within the scope of usable compounds, the formersilica or even extra zirconium oxide with the result that the sintered product may not correspond precisely witheither of the formulas given but such compositions may be used provided in all cases they fall within the defined limits for the several oxides given hereinabove.

In tanning, the double silicates are introduced into the: acid liquor with the skin and it has been found that the double silicate is gradually decomposed by the acid present into compounds at least one of which is a zirconium salt which dissolves in the acid tanning liquor and reacts. with the protein of the skin substantially as rapidly as: the zirconium salt is liberated. This decomposition by the acid is slow and it may take several hours for the complete conversion of the double silicate into the dissolved zirconium compound or compounds which react with leather. The result is a gradual tannage which assures penetration and avoids too quick a tannage of the surface of the skin which might hinder penetration of tanning agent. It may be that the beneficial action is partly attributable to this slow gradual formation of the soluble zirconium compounds during the drumming of the skin therein.

The tanning liquor comprises Water, a salt, the insoluble double silicate of an alkali metal and zirconium in pulverized form, and sufiicient acid, preferably a strong mineral acid, equivalent to that needed to provide the corresponding zirconium salt of 060% basicity by the Schorlemmer scale. Preferably the acid is used in an amount to provide a basicity of 25-50%, the range of 40-50% basicity being more economical by virtue of the reduction in amount of neutralizing material needed to be added later after the completion of tannage.

Various salts may be used such as sodium chloride, sodium sulfate or the like. Generally when the acid used is sulfuric acid, the salt preferably is sodium chloride, Whereas if the acid used is hydrochloric acid, the salt is preferably sodium sulfate. The tanning liquor preferably contains from 3-10% of the salt based on the total weight of the liquor. From 520% by weight of the'pulverized double silicate of zirconium and alkali metal,

. based on the Weight of the skin, is used. To obtain a full tan, 12-15% by weight of the double silicate based on the Weight of the skin is generally adequate. The entire amount of the double silicate need not be added at the start of the tannage, but it may be added in portions at intervals of /1 to /2 hour.

into the liquor before any of the ingredients have been i added except the salt. It is necessary, however, at least to have the salt dissolved in the liquor before the skin is introduced to prevent swelling of the pickled skin. In the latter event, either the acid or the double silicate of zirconium may be added before the other. As pointed out hereinbefore, the double silicate may be added in portions, but for convenience it is preferred to add the entire amount of double silicate at the start and at one time.

The tanning is effected with the liquor at about room temperature up to but not over 35 C. When, in making up the tanning liquor, the temperature thereof rises above 35 C., it should be cooled at least to 35 C. and preferably to 2530 C. before introducing the skin.

A dry tanning composition may be produced by mixing the pulverized double silicate of zirconium with the appropriate amount of dry acidic material, such as sulfamic acid or sodium bisulfate. Such dry composition, if stored in dry containers, is stable for a considerable time and may be shipped and stored until it is desired for tanning use. Our eopending application Serial No. (197,526, filed November 20, l957, describes and claims these dry compositions.

The following examples are illustrative of the invention:

Example 1 Ten pounds of sodium chloride, 23.5 pounds of 50% sulfuric acid, and water to make 200 pounds total water wcreintroduced into a tanning drum. The mixture was drummed and cooled to 30 C. and then there were added fourteen pounds of a powdered sodium zirconium silicate having approximately a composition corresponding to the formula Na ZrSiO obtained by sintering one mole of zircon sand (ZrSiO with one mole of sodium carbonate and grinding. One hundred pounds of pickled calfskins having a pH of 2 were immediately introduced and drummed for 6 hours. The skins were left in the liquor overnight at a pH of 1.5 to 2. The next day they were neutralized in the same liquor with 3% sodium acetate and about 4% sodium bicarbonate to a pH of 4.5 to 4.75. The skins were then washed, fatliquored, and finished as usual. The dry leather obtained was a white leather having a plump and mellow feel.

Example 2 The procedure of Example 1 was followed except that the skins were introduced into the cooled acid liquor about /2 hour before the sodium zirconium silicate was added. After drumming 4 /2 hours, the procedure of Example 1 was followed with similar results.

Example 3 The procedure of Example 1 was followed except that 30 pounds of niter cake were substituted for the sulfuric acid. A good quality leather was obtained.

Example 4 The procedure of Example 1 was followed except that 25 pounds of sulfamic acid was substituted for the sulfuric acid. A good white, plump and mellow leather was obtained.

Example 5 The procedure of Example 1 was followed except that the sulfuric acid was replaced with 24 ponnds of 37% hydrochloric acid and the common salt was replaced with 25 pounds of anhydrous sodium sulfate. A good white, plump leather was obtained.

Example 6 The procedure of Example 1 was followed except that the process may be applied to sheepskins, skivers, pigskins, cowhides, horsehides, goatskins and so on.

While the general purpose and special advantage of zirconium tanning is to produce white leathers, the present invention is adaptable to the production of colored leathers as well. To do this, after neutralization at the end of the tannage step, the leather may be colored by acid or direct dyes by customary methods, then fatliquored before drying out.

The leather may be tanned by the sodium zirconium silicate alone or it may be subjected to a two-stage tannage'in which the zirconium silicate is used before or after tannage with chromium, iron, aluminum, vegetable tans, syntans or formaldehyde. Alternatively, the leather may be treated in a single-stage combination tannage involving the use of the sodium zirconium silicate in the same tanning bath with other mineral tanning agents, such as chromium.

The procedure of the present invention is simple and inexpensive since it uses inexpensive double silicates of zirconium, and his unnecessary to convert the double silicate into water-soluble zirconium salts before applying the tanning liquor containing the water-insoluble zirconium compound to the skins. The process of the present invention also avoids the necessity of producing water-soluble zirconium compounds within silica gel sheaths or of using organic compounds of the hydrogen bonding donor type. Not only is the process a simple and inexpensive way of tanning with zirconium, but it produces tanned leathers which are fully equivalent in quality, and in some cases of better quality, than leathers previously produced with water-soluble zirconium compounds.

it is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined in the appended claims.

We claim:

l. A process of tanning a skin comprising tanning the skin in an aqueous solution of an acidic material selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, sodium acid sulfate, and sulfamic acid, at a temperature not over 35 C., containing suspended therein a pulverized water-insoluble double silicate of zirconium and an alkali metal M in which the molar ratio SiO :ZrO is from about 1:1 up to but not over 1.5 :1 and the molar ratio SiO :M O is from about 1:1 up to but not over 3:1, the acidity being adjusted to provide the corresponding salt of zirconium of zero to 60% basicity calculated on the Schorlemmer scale upon complete dissociation of the sodium zirconium silicate, the skin remaining in this tanning liquor until it is tanned to the desired extent.

2. A process of tanning a skin comprising tanning the skin in an aqueous acid solution of an acidic material selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, sodium acid sulfate, and sulfamic acid, at a temperature not over 35 C., containing suspended therein a pulverized water-insoluble double silicate of zirconium and an alkali metal M in which the molar ratio SiO :ZrO is about 1: 1 and the molar ratio SiO :M O is about 1:1, the acidity being adjusted to provide the corresponding salt of zirconium of zero to 60% basicity calculated on the Schorlemmer scale upon complete dissociation of the sodium zirconium silicate, the skin remaining in this tanning liquor until it is tanned to the desired extent,

3. A process of tanning a skin comprising tanning the skin in an aqueous acid solution of an acidic material selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, sodium acid sulfate, and sulfamie acid, at a temperature not over 35 0., containing suspended therein a pulverized water-insoluble sodium zirconium silicate of the formula Na ZrSiO the acidity being adjusted to provide the corresponding salt of zirconium of zero to 60% basicity calculated on the Schorlemmer scale upon complete dissociation of the sodium zirconium silicate, the skin remaining in this tanning liquor until it is tanned to the desired extent.

4. A process of tanning a skin comprising preparing an aqueous solution of an acid selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, sodium acid sulfate, and sulfamic acid and about 3% to about of a water-soluble alkali metal salt which prevents swelling of pickled skins, the alkali metal being the sole metal in said alkali metal salt, then introducing into the solution at a temperature below 35 C., the skin and a pulverized Water-insoluble double silicate of zirconium and an alkali metal M in which the molar ratio SiO :ZrO is from about 1:1 up to but not over 1.5 :1 and the molar ratio SiO :M O is from about 1:1 up to but not over 3:1, the acidity being adjusted to provide the corresponding salt of zirconium of zero to 60% basicity calculated on the Schorlemmer scale upon complete dissociation of the sodium zirconium silicate, the skin remaining in this tanning liquor until it is tanned to the desired extent.

5. A process of tanning a skin comprising preparing an aqueous solution of an acidic material selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, sodium acid sulfate, and sulfarn-ic acid and about 3% to 10% salt selected from the group consisting of watersoluble alkali metal chlorides and sulfates, introducing into the solution, at a temperature not over 35 C., a pickled skin having a pH of about 1.5 to 2, and then introducing into the liquor thus obtained 5% to by weight, based on the skin weight, of a pulverized water-insoluble sodium zirconium silicate in which the molar ratio siO zZrO is from about 1:1 up to but not over 1.5:1 and the molar ratio SiO :Na O is from about 1:1 up to but not over 3: 1, the amount of said acid being adjusted to provide the corresponding salt of zirconium of zero to 60% basicity calculated on the Schorlemmer scale upon complete dissociation of the sodium zirconium silicate, the skin remaining in this tanning liquor until it is tanned to the desired extent.

6. A process of tanning a skin comprising preparing an aqueous solution of an acidic material selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, sodium acid sulfate, and sulfamic acid and about 3 to 10% salt selected from the group consisting of watersoluble alkali metal chlorides and sulfates, introducing 5 to 20% by weight, based on the weight of skin to be treated, of a pulverized Water-insoluble sodium zirconium silicate in which the molar ratio SiO :ZrO is from about 1: 1 up to but not over 1.5 1 and the molar ratio Sio zNa O is from about 1:1 up to but not over 3:1, the amount of said acidic material being adjusted to provide the corresponding salt of zirconium of zero to basicity calculated on the Schorlemmer scale upon complete dissociation of the sodium zirconium silicate, then introducing into the liquor thus obtained while it still contains pulverized silicate suspended therein, at a temperature not over 35 C., a pickled skin having a pH of about 1.5 to 2, and maintaining the skin in the solution, at a temperature not over 35 C., until the skin is tanned.

7. The process as defined in claim 6 in which the acidic material comprises sulfuric acid and the salt comprises sodium chloride.

8. The process as defined in claim 6 in which the acidic material comprises sulfuric acid, the salt comprises sodium chloride, and the silicate has the formula Na ZrSiO 9. The process as defined in claim 6 in which the acidic material comprises hydrochloric acid and the salt comprises sodium sulfate.

10. The process as defined in claim 6 in which the acidic material comprises sulfamic acid and the salt comprises sodium chloride.

11. The process as defined in claim 6 in which the acidic material comprises nitric acid and the salt comprises sodium sulfate.

12. A process of tanning a skin comprising preparing a liquor comprising an aqueous solution of 3 to 10% of sodium chloride and 4 to 17% of sulfuric acid, introducing about 5% to 20% by weight of pulverized water-insoluble sodium zirconium silicate of the formula Na ZrSiO and then tanning a skin with the resulting tanning liquor while it still contains pulverized silicate suspended therein, at a temperature not over 35 C.

References Cited in the file of this'patent UNITED STATES PATENTS 2,689,163 Paquet Sept. 14, 1954 FOREIGN PATENTS 917,317 France Sept. 9, 1946 

1. A PROCESS OF TANNING A SKIN COMPRISING TANNING THE SKIN IN AN AQUEOUS SOLUTION OF AN ACIDIC MATERIAL SELECTED FROM THE GROUP CONSISTING OF SULFRIC ACID, HYDROCHLORIC ACID, NIYTRIC ACID, SODIUM ACID SULFATE, AND SULFAMIC ACID, AT A TEMPERATURE NOT OVER 35*C., CONTAINING SUS PENDEDTHEREIN A PULVERIZED WATER-INSOLUBLE DOUBLE SILICATE OF ZIRCONIUM AND AN ALKALI METAL M IN WHICH THE MOLAR RATIO SIO2:ZRO2 IS FROM ABOUT 1:1 UP TO BUT NOT OVER 1.5:11 AND THE MOLAR RATIO SIO2:M2O IS FROM ABOUT 1:1 UP BUT NOT OVER 3:1, THE ACIDITY BEING ADJUSTED TO PROVIDE THE CORRESPONDING SALT OF ZIRCONIUM OF ZERO TO 60% BASICITY CALCULATED ON THE SCHORELEMER SCALE UPON COMPLETE DISSOCIATION OF THE SODIUM ZIRCONIUM SILICATE, THE SKIN REMAINING IN THEIS TANNING LIQUOR UNTIL IT IS TANNED TO THE DESIRED EXTENT. 